1. Field of the Invention
This invention relates to a verifying system for verifying a shut-off state of a hot gas flow passage, and, in particular, to a valve operation verifying system for verifying opening and closing operation of a gas flow control valve of a type having a valve body and an elastic body deformable in response to engine operating conditions to force the valve body to control amounts of gas admitted to flow through a hot gas flow passage, such as an exhaust gas recirculation passage of an exhaust gas recirculation system installed on an automobile engine.
2. Description of the Related Art
Typically, fluid flow passages are variably opened and closed by a regulation valve which is forced by an elastic body deformable in response to changes in pressure. As shown in, for example, Japanese Unexamined Patent Publication No. 6-58210, such a regulation valve is installed in the form of pressure modulated exhaust gas recirculation valve to a hot exhaust gas recirculation passage to control amounts of exhaust gas that is recirculated into an intake air stream. The Japanese Unexamined Patent Publication No. 6-58210 mentioned above also teaches verification of opening and closing valve operation of the exhaust gas recirculation valve on a basis of a change in gas pressure in the exhaust gas recirculation passage caused before and after momentarily opening or closing of the exhaust gas recirculation valve. In the cases where the gas circulation passage incorporates an exhaust gas recirculation valve of the type having a valve body and an elastic body which is elastically deformable to force the valve body to open and close the exhaust gas recirculation passage, verification of opening and closing operation of the exhaust gas recirculation valve is interrupted while the temperature of ambient air is lower than a specified temperature of, for example, 10.degree. C., which is a critical point for low temperature hardening of the elastically deformable body, and in such cases the verification of the opening and closing of the valve operation is inaccurate.
Even if the temperature of ambient air is low and the elastic body possibly loses its specified elasticity or flexibility, the elastically deformable body incorporated in the exhaust gas recirculation passage can be warmed up with hot exhaust gas somewhat sufficiently to be elastically deformable or flexible as specified, in the event of which unconditional interruption of the verification of valve operation results in less chance to execute the verification of valve operation and causes a problem in the early detection of an operational failure of the exhaust gas recirculation valve.